The present invention relates to a speed control system for a rotary distributor having multiple distribution arms that distribute waste water over a porous media of a trickling filter by discharging it through ports or nozzles spaced along the length of each distribution arm. The rotary distributor of the present invention uses hydraulic forces to control the rotational speed of the distribution arms.
Currently, when speed control is used, motor driven rotary distributors are commonly used to distribute waste water over porous media in trickling filter applications. A motor driven rotary distributor has a motor driven gear reducer that is mounted on the center column of the rotary distributor or on the end of one of the distribution arms. The motor has an adjustable speed controller so that the rotary distribution arms can be rotated at various desired speeds. When using a motor driven gear reducer, the hydraulic thrust normally associated with rotary distributors is nulled out by balancing the forward and reverse discharge from the arms so as to have a configuration that yields a near net zero thrust.
One disadvantage with motor driven rotary distributors is that they require significant amounts of energy from an outside source. Another disadvantage with motor driven rotary distributors is that larger units with higher flow rates become difficult to start and stop without damaging equipment.
Because the distribution arms are filled with water and may be up to 100 feet long, their mass creates a high moment of inertia that can lead to operating problems. When the arms are initially rotated from a rest condition, the strain placed on the gear reducer is significant, particularly if the acceleration is excessive. Therefore, the acceleration must be carefully controlled to prevent premature failure of the gear reduction mechanism. Conversely, if deceleration is not carefully controlled, the gear reducer can fail prematurely due to the friction, viscous drag and inertia of the motor and drive components. An over torque condition can destroy various parts of the system if an arm is caught on an obstruction. All of these potential problems can create situations where the treatment equipment is out of commission for an extended period, which may occur at an inappropriate time.
Prior to the addition of motor drives to rotary distributors, the distribution arms were designed to be rotatively driven by the hydraulic thrust produced by the discharging water. However, controlling the speed ofthe arms was difficult because it involved manually repositioning spreaders and caps along each arm so as to change the amount of forward and reverse discharge exiting the arms. Still another disadvantage with these manually controlled rotary distributors is that slow operating speeds, which sometimes are desirable, are difficult to achieve reliably because wind forces may work against the speed of the arms. In addition, a period of lower flows can cause the arms to stop moving when they are operating at low operating speeds, which is detrimental to the trickling filter performance.
In order to overcome these disadvantages, an improved speed control system for a rotary distributor is needed. This speed control should be able to use hydraulic forces to control the rotational speed of the distribution arms of the rotary distributor, thereby taking advantage of the hydraulic energy already present and eliminating the need for additional power.